PERMANENT 3-DIMENSIONAL PATTERNS IN TURBULENT FLOWS WITH ESSENTIALLY 2-DIMENSIONAL WALL CONFIGURATIONS

The phenomenon of steady three-dimensional structures transverse to th e main Bow direction in turbulent Bows with mainly two-dimensional wal l configurations has been investigated. Time invariant two-dimensional temperature distributions in an asymmetrically ribbed channel have be en detected by infrared thermography and are compared with published d ata of three-dimensional Row structures in turbulent boundary layers a bove a single rectangular cavity and a single rib inside a turbulent c hannel flow, respectively. The periodic length of the observed Bow str uctures correlate quite well among different investigations, although methods of investigation and boundary conditions are different. It can be concluded that such structures in turbulent flows with nearly two- dimensional boundary conditions (large aspect ratio of the cross-secti on) are self-sustaining flow effects. No physical explanation of the o rigin of this phenomenon and of the observed dependencies on the wavel ength are available yet.